Table 2

Colistin MICs for subset of isolates that tested as nonsusceptible at time of isolation (phase I) and/or showed major or very major errors in either phase I or phase II with BMD-T as the reference method

Isolate no.aOrganismMIC (μg/ml)b
Phase I (n = 107)Phase II (n = 50)
1*A. baumannii441b0.58c0.51
2A. baumannii8161.5b>8>8>16>4
3A. baumannii>882b>8>884
4A. baumannii8>163>8>8>16>4
5A. baumannii>8160.5bNDdNDNDND
6A. baumannii>8163NDNDNDND
7A. baumannii>81612NDNDNDND
7AA. baumannii24c224c21
8K. pneumoniae>8>168>8>8>16>4
9K. pneumoniae>8>1612>8>8>16>4
10K. pneumoniae>8>1648>8>8>16>4
11K. pneumoniae>8>160.5b>8>8>16>4
12K. pneumoniae>8>168>8>8>16>4
13K. pneumoniae480.5b82b44
14*K. pneumoniae4830.25210.5
15*K. pneumoniae>8>1612≤0.120.5≤0.25ND
16K. pneumoniae886NDNDNDND
17*P. aeruginosa816328c4c>4c
18P. aeruginosa213c4>82b>4
19*P. aeruginosa44424c4c2
20P. aeruginosa883NDNDNDND
21P. aeruginosa0.2514cNDNDNDND
22P. aeruginosa0.50.53c0.511ND
23P. aeruginosa24c224c4c2
24P. aeruginosa0.524cNDNDNDND
25P. aeruginosa110.51224c
No. of VMEs (%)0 (0)6 (32)1 (10)0 (0)0 (0)
No. of MEs (%)2 (2.3)4 (4.7)5 (12.5)3 (7.5)2 (5)
% EA8361348062
% CA9891889496
  • a Isolate numbers marked with an asterisk indicates isolates that lost resistance following storage and were discovered in phase II testing.

  • b Very major errors (VMEs) were calculated with 19 (phase I) or 10 (phase II) resistant (MIC, >2 μg/ml) isolates as the denominator.

  • c Major errors (MEs) were calculated with 88 (phase I) or 40 (phase II) susceptible (MIC, ≤2 μg/ml) isolates as the denominator. Essential agreement (EA) and categorical agreement (CA) were calculated with 107 (phase I) or 50 (phase II) isolates as the denominator.

  • d ND, not done, as isolates were unavailable for phase II testing.